BA-53635/PLMD
From Halopedia, the Halo wiki
The BA-53635/PLMD the a United Nations Space Command integrated non-replaceable battery for the Weapon/Anti-Vehicle Model 6 Grindell/Galileian Nonlinear Rifle (W/AV M6 G/GNR) "Spartan Laser" weapon.
It powers the Spartan Laser's blood red laser beams, which are incredibly vast in power and can destroy any enemy: infantry or vehicular, upon a single impact. However, the energy consumption for the M6 G/GNR is expectedly extreme, and the BA-53635/PLMD battery is drained in five laser shots.